无法使用改造在ListView中显示数据

Question

I 've problem with display data in ListView. I get data from Retrofit response, but my activity, which should display this data, is just beeing blank, all the time. I am sure, that I've receiving data, I've checked it, in console.

Model class

public class itemList_model {
@SerializedName("results")
private List<itemList_Results> results;

public List<itemList_Results> getResults() {
    return results;
}

public static class itemList_Results{
    @SerializedName("title")
    String title;
    @SerializedName("vote_average")
    Double vote;
    @SerializedName("genre_ids")
    List<Integer> genresId;
    @SerializedName("release_date")
    String releaseDate;

    public itemList_Results(String title, Double vote, String releaseDate) {
        this.title = title;
        this.vote = vote;
        this.releaseDate = releaseDate;
    }

    public String getTitle() {
        return title;
    }

    public Double getVote() {
        return vote;
    }

    public List<Integer> getGenresId() {
        return genresId;
    }

    public String getReleaseDate() {
        return releaseDate;
    }
}

public class itemList_genresId{
    @SerializedName("genre_ids")
    int id;

    public int getId() {
        return id;
    }
 }
}

adapter class

public class genres_adapter extends ArrayAdapter<itemList_model.itemList_Results> {
RetrofitCalls calls;

public genres_adapter(@NonNull Context context, ArrayList<itemList_model.itemList_Results> list) {
    super(context, 0, list);
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    View itemView = convertView;
    if (itemView == null){
        itemView = LayoutInflater.from(getContext()).inflate(R.layout.genres_item_view, parent, false);
    }
    itemList_model.itemList_Results model = getItem(position);

    TextView title = itemView.findViewById(R.id.title);
    title.setText(model.getTitle());
    TextView vote = itemView.findViewById(R.id.vote);
    vote.setText(String.valueOf(model.getVote()));
    TextView release = itemView.findViewById(R.id.release);
    release.setText(model.getReleaseDate());
    return itemView;
 }
}

activity java class

ArrayList<itemList_model.itemList_Results> arrayList;
genres_adapter adapter;

String title = "";
Double average_votes = 0.0;
String date = "";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_genres_list_view);

    arrayList = new ArrayList<itemList_model.itemList_Results>();
    adapter = new genres_adapter(this, arrayList);

    ListView listView = (ListView) findViewById(R.id.genres_listView);
    listView.setAdapter(adapter);
    getListViewItems();
}
public void getListViewItems(){

    String url = "https://api.themoviedb.org/";
    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(url)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

    apiCall api = retrofit.create(apiCall.class);
    Call<itemList_model> call = api.getHorror();
    call.enqueue(new Callback<itemList_model>() {
        @Override
        public void onResponse(Call<itemList_model> call, Response<itemList_model> response) {
            if (!response.isSuccessful()) {
                Log.i(TAG, "onResponse: " + response.code());
            }
            List<itemList_model.itemList_Results> list = response.body().getResults();
            for (itemList_model.itemList_Results model : list){

                title =model.getTitle();
                average_votes = Double.valueOf(model.getVote());
                date =model.getReleaseDate();
            }
            list.add(new itemList_model.itemList_Results(title,average_votes,date));
        }
        @Override
        public void onFailure(Call<itemList_model> call, Throwable t) {
            Log.i(TAG, "onFailure: "+t.getMessage());
        }
    });
}

• activity, that contains ListView, is called activity_genres_list_view
• activity which will be used by adapter, is called genres_item_view

I'm guess, it's about data from list, maybe it's not being added?

Answer 1

显然，您应该在收到列表后将其添加到适配器：

adapter.addAll(list);

Answer 2

I cannot see any notifyDataSetChanged() call in your code. When the response is found from the Retrofit call, you need to update the list which was passed to the adapter and call notifyDataSetChanged on your adapter to see the effect.

Hence you might consider doing something like the following.

public void getListViewItems(){

    String url = "https://api.themoviedb.org/";
    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(url)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

    apiCall api = retrofit.create(apiCall.class);
    Call<itemList_model> call = api.getHorror();
    call.enqueue(new Callback<itemList_model>() {
        @Override
        public void onResponse(Call<itemList_model> call, Response<itemList_model> response) {
            if (!response.isSuccessful()) {
                Log.i(TAG, "onResponse: " + response.code());
            }

            // Do not create a new list here. Use the arrayList which was declared before and passed to the adapter
            // List<itemList_model.itemList_Results> list = response.body().getResults();

            // Clear the arrayList before pushing new data
            arrayList.clear();

            for (itemList_model.itemList_Results model : list){
                title =model.getTitle();
                average_votes = Double.valueOf(model.getVote());
                date = model.getReleaseDate();

                // Add the data into the arrayList instead of the list
                arrayList.add(new itemList_model.itemList_Results(title,average_votes,date));
            }

            // Now call notifyDataSetChanged on your adapter to see the changes in the ListView
            adapter.notifyDataSetChanged();
        }

        @Override
        public void onFailure(Call<itemList_model> call, Throwable t) {
            Log.i(TAG, "onFailure: "+t.getMessage());
        }
    });
}

Hope that fixes your problem.

Answer 3

Nothing appear because you are setting adapter before getting information :

    adapter = new genres_adapter(this, arrayList);//array list is still empty here
    listView.setAdapter(adapter);
    getListViewItems();

what yo should do is setting adapter once you get the list ! or call notifydatasetChanged on your adapter after you get your informations !

{
.....
arrayList.add(new itemList_model.itemList_Results(title,average_votes,date));
.....
}
adapter.notifyDataSetChanged();